Method for refining lubricating oil distillates



' crease the volume somewhat into the 100 to 500% The amount of thetreating agent should Patented Oct. 8, 1940 UNITED METHOD FOR REFININGLUBRIOATING 01L DISTILLATES I Hans G. Vesterdal, Elizabeth, N. J.,assignor to Standard Oil Development Company, a corporation of DelawareNo Drawing. Application May 28, 1938,- Serial No. 210,749

6 Claims.

The present invention relates to an improved method for refining heavyhydrocarbon oils, especially' of the type obtained from naphtheniccrudes,which are susceptible to loss of color on standing or whichcontain impurities such as soaps having high ash contents, The inventionwill be fully understood from the following description.

Lubricating oil distillates are frequently susceptible to loss in coloron standing. This appears to be a marked characteristic of the productsderived from naphthenic base crudes such as are obtained from Colombiaand the Coastal regions of the United States. These oils are largelyused for making low cold test lubricants for industrial purposes. Thecause of the loss of color is not fully understood, but it is believedto be due to the presence of small amounts of naphthenic acids andfrequently to the presence of complex phenolic materials. It is nowcustomary to refine these oils by treatment with acid but in order toobtain color stable oils according to this method, large amounts ofsulfuric acid are required in the treatment and the treating loss isquite large. Residual oil containing soaps and having high ash contentare also troublesome to handle by present methods, which givesatisfactory products only at the cost of a considerable loss of oil. Ithas been found that oils of these types can be readily refined Withoutany acid treatment whatever and they are satisfactory for most of thepurposes to which they are now put. If better oils are required, alimited acid treatment or solvent extraction treatment or other refiningmethod may be used such as limited oxidation which are followed, ifdesired, with either acid or solvent refining. These various refiningmethods are used prior to the present finishing process but'for mostpurposes this is not required. In the present process, the oil, whethera crude or a distillate or residue obtained by pipe still distillationor residue obtained in distillation over caustic soda, is treated underhigh temperature with say 10 to 500% of its volume of a dilute aqueouscaustic alkali, preferably sodium hydroxide.

The concentration of the alkali may be from .25 to 5% depending to someextent on the character of the oil to be refined, its viscosity, and theamount of impurity to be removed. It is preferred to use solutions inthe more dilute portion of the range specified hereinabove, and thevolume used is preferably 10 to 100% of the oil to be treated, but whenthe amount of the extractable materials is high, it is preferable toinrange. be such as to form a dilute solution of the extractables forexample less than 10% soap so as to avoid loss of oil inthe treatingsolution. The

extractable materials are more soluble in and therefore more readilyremovable by dilute rather than more concentrated soda solutions. Thetreatment is accomplished at temperatures above about 350 and preferablybelow about 500 F. 1

so as to avoid thermal decomposition. The more viscous the oil thehigher the treating temperature will be to get a clear separation.Pressure is sufficiently high to prevent evaporation of the water fromthe treating solution. Residues which are solid at room temperatures maybe successfully treated to remove salt, soaps, and the like.

The temperature should be kept well up within the range specified and ifallowed to fall below about 350 F., there is found to be troublesomeemulsification which prevents a clean separation of the aqueous from theoily layers. A small amount of oil will usually be included with theaqueous layer, which is removed while hot, but great care should beexercised to remove as completely as possible all traces of the aqueousfrom the oily layer. If this is carefully carried out under theconditions set forth above, no further purification of the oil isrequired. Water washing or cooling before separation of the water andoil layers should be avoided since this causes hydrolysis of the sodacompounds of the extractable materials and causes the finished oil tohave high neutralization value.

If the oil distillate is freshly obtained from crude stills while itstill has a good color and is immediately subjected to the treatmentwith the dilute caustic alkali, no further treatment is required, but itis found that the distillate goes off color rapidly on standing and toobtain a finished oil'of good color, it is often necessary to redistillthe oil after the caustic treatment. The distillation is preferablycarried out under vacuum in order to avoid decomposition. Whentreatingiuel oils color and color hold are unimportant but the treatmentis very effective in reducing ash content which is of great importance.

Frequently when such residues are obtained by distillation over causticsoda there is enough soda present so that Water may be used as thetreating agent and the caustic solution is formed in situ.

The caustic treatment is capable of removing materials which cause theoil to go off in color on standing, but once these materials havedeveloped color, the treatment is not effective in restoring color anddistillation must be resorted to. The treatment may be in batch orcontinuous,- using counterfiow or parallel flow.

' The caustic soda may be recovered mainly by cooling to roomtemperature whereupon the extracted material or a large part thereofsettles out apd the causticmay be reused many times,

only a small amount of make up being required before it must bereplaced.

As examples of the operation of the present process, the following -maybe considered:

EXAMPLE 1 A light Colombian lubricating oil distillate was heated in aclosed pressure vessel with 25% of its volume of 2% aqueous caustic sodato a temperature of 400 F. A pressure of 250 pounds per square inch wasmaintained in the vessel so as to prevent evaporation of thecausticsolution and the mixture was agitated until'tho'rough contact wasassured. The mixture was then allowed to stratify, which it did cleanly,and the aqueous liquor was drawn 011 while hot. The oil was redistilledunder Vacuum without any further treatment, giving 5.5% of light endsand 9 1% of a refined lubricating oil distillate.

The inspection of the original oil and the extracted and r'edistilledproducts is as follows:

The average lubricating oil standard is a measure of the color stabilityof an average lube oil, as determined on hundreds of samples ofcommercial lube oils. Thus an average lube oil having an initial colorof 4% Robinson would have a color of 2 Robinson on heating in presenceof air at 250 F. for 16 hrs., and one of 8 color would drop to 4R+ inthe same test. The caustic treated oils are thus considerably betterthan the average oils.

Washed Washed bWith150% bwith150% Orig- Redisg; Y a o aq. of 3% aq. malon tluvd caustic at caustic at 400 F. and 400 F. and

redistilled redistilled Percent cut 100 0-98 0-94 0-97 1S./100 F 274Color, Robinson Dark 6 9% 8% Color after 16 hrs. at

250 F i 1 7% 4% Average lubricating oil standard 3+ 5% 4% 2. 15 2. 15 0.08 0. 09 2. 30 2. 30 0. 14 0. 28

By the usual acid treating method used,'the yield of color stablerefined oil from this stock is only about but the yield obtained bythe'present method averages about 10% higher for similar or betterquality.

EXAMPLE 3 A total Colombian lube cut was extracted countercurrently in atower with 78% of its volume of 0.45% aqueous caustic solution at anaverage tower temperature of 385 F., keeping sufficient nitrogenpressure on the system to prevent boiling of the water and in anotherexperiment the total Colombian lube out was extracted with 88% of itsvolume of 3.84% aqueous caustic solution 30 at an average towertemperature of 385 F. Good separations of caustic extract and oil wereobtained. The oils were fractionated under vacuum and separated intoseveral cuts. of the cuts and of the untreated oil is as follows:

' Color Average Percent Color Neut.

V1s./100 hold 16 hrs. lube oil cut Robmson at 250 F. standard Originaloil 100 342 Black 2. 23 0-30 86 16% 16% 11+ 0. 05 Extracted once with78% of 0.45% caustic at 30-50 239 10% 9% 9+ 0.08 385 F., and rerun 50-70576 8% 8% 4% 0.09 70-90 1200 8 3% 4 0. 09 0-30 84 17 13% 11% 0. 01Extracted once with 88% of 3.84% caustic at 30-50 243 10% 9% 8% 0.04 385F., and rerun N 50-70 585 9% 6% 5% 0. 09 70-90 1235 8% 2% 4 0. 11

EXAMPLE 2 EXAMPLE 4 A medium Colombian distillate having a Viscosity of274 seconds Saybolt at 100 F., was extracted with 50% or its volume ofdilute caustic solution at 400 F., in the same man'nerdescribed inExample 1, using a 2% caustic solution in one case and a 3% causticsolution in another case. In both cases the oil separated readily fromthe caustic solutions on settling at 400 F., for 5 to 10 minutes. Theoils were redistilled under vacuum A wide cut Sugarland lube distillatehaving a The inspection viscosity at 100 F., of 196 seconds Saybolt was3 extracted twice in a countercurrent tower at an average towertemperature of 385 F., using 80% of its volume of 2% aqueous causticsolution in each treat. The original oil, and the caustic treated oil,were fractionated under vacuum and 55 separated into 10% cuts.

Inspections of these cuts were as follows:

Color after Average Percent Color Neut.

V1s./100 16 hrs. at lube 011 cut Robinson Standard No. 0

Original oil -4 100 39- 2 1 3 0.92 0-10 39. 2 21% 19 0. 28 10-20 53. 918% 17% 13% 0. 52 20-30 77 17 11% 11% O. 80 30-40 118 16% 10% 11 0. 6 5Vacuum fractionated 40-50 196 13% 9 10 0.98 v I 1 50-60 338 8% 9; 0.9560-70 617 10% 5 8 0. 92 70-80 1120 9 4% 4% 0. 88 80-90 1088 8% 3 4+ 0.86 0-10 39. 8 21% 18% 0. 03 10-20 55. 0 18% 17% 12%+ 0. 03 20-30 78. 417 14% 11% 0. 05 70 Sample vacuum fractionated after 2 x 80% 30-40 25 6%12 05 countercurrent treats with 2% caustic at 40-50 210 14% 10 10% 0.06385 F 50-60 340 12% 9% 9% 0. 06 60-70 600 10% 9 9+ 0.08 70-80 1080 9% 65% 0. 11 89-90 1627 8% 4% 4+ 0. 14

In this case even'the cutsfroin' the untreated oil were fairly colorstable especially the-light viscosity ones, but caustic treatingimproved-the color stability considerably. The treatment wasparticularly effective with the 1000 to 1600 viscosity cuts (70-80% and89-90%) which were color stable while the untreated ones were not.

EXAMPLE 5 A light Colombian lube distillate was treated with 15 poundsof 91% sulfuric acid at about F. On settling, the sludge was drawn ofiand the oil was neutralized with caustic. The neutral oil so obtainedwhich contained about 0.02% excooling the caustic extracts to roomtemperature or lower, practically all the extracted material separatesout of solution, leaving a recovered caustic which may be used overagain. In

order to prove that the recovered caustic is' just Oil treated withrecovered caustic and redistilled I Oil treated with fresh causticO11650Z 2011 Two counter current treats tercurrent rea a One 38%countercurrent Y treat at 3804300 F at 380390 F. (38+25% to 390 F.

treats) CutNo 1 2 3 4 1 2 3 4 1 2 a. 4

ViS./ 75.7 213 545 1301 79.1 221 555 1318 77 220 531 61298 Color,Robinson 11 9 7 16% 10% 9 7% 16% 11% ,9; 7% Color after 16 hrs. at 2509% 4% 2% 1214 9 5% 254 163 9% 5 1% Average lube oil standard. 9% 434+3%,, 11+ 9 454+ 3%+ 11% 934+ 4B4. 3% Neut.No .05 .06 .09 .12 .03 03 v.05.08 .05 .05 .08 .11

cess caustic was distilled under vacuum in a re- EXAMPLE 7 finery pipestill, and another sample of the same oil Was washed twice in a bombwith 25% of its volume of 2% caustic each time, at 400 F., and stillanother sample was washed twice with 50. of its volume of water eachtime at 460 F. Both the samples of washed oils were vacuum distilled ina laboratory still. Ash contents of the oils before distillation were asfollows:

Per cent ash Acid treated and neutralized oil 0.65

Acid treated and neutralized oil washed with caustic at 400 F 0.008

Acid treated and neutralized oil washed with water at 460 F 0.04

Inspection of the distillates obtained from these oils was as follows:

Acid treated and neutralized A sample of pipe still bottoms obtained onstripping 01f the lubricating oil distillates from an acid treated andneutralized Colombian distillate in a refinery pipe still was washedwith dilute caustic at 470 F. Analysis of the original pipe stillbottoms showed that it had approximately the following composition:

Per cent Heavy oil 50 Inorganic salts 6 Soaps (by diiference) 44 and theash content was 12.89%

On washing these bottoms with 300% of its volume of 0.5% caustic at 470F. by mixing thoroughly in a closed bomb under equilibrium pressure for30 minutes, followed by settling for 5 minutes, a clear separation ofoil and extract was obtained. 42 volumes of oil were recovered fromlight Colombian distillate Washed with 2% caustic at Washed with waterat 460 Fractlonatedlnre- 400 F. (2x25% treats) F. (2x50% treats andfinery pipe still and iractlonated in the fractionated in thelabolaboratory ratory Vis./l00 72.3 240 908 71.2 211 344 903 76.5 236514 997 Color, Robinson 173 2 11% 8% 17% 14% 11% 8% 17 12% 9% 6V golorafterblfi hiiistat (215031 1%? gyi 2% 103% 32% y? 16% 1034 8% 2 4 verageu e0 s an ar z 4 2 9 4 11 .9 5 3 Nent. No 0. 04 0.05 0 0s 0. 04 0.040.07 0.0% 0. a? 1.1 6

It will be noted that on washing with water at 460 F., theneutralization values of the distillates were very high, showing thatthe soaps had been hydrolized to a large extent, whereas the very lowash content (0.008%) of the caustic washed oil and the lowneutralization values of the distillates show that the soap was washedout thoroughly with 2% caustic solution at 400 F.

EXAMPLE 6 When using large volumes of caustic solution for extractionsof acids and unstable compounds from petroleum oils, it is necessary torecover the excess caustic. This is easily done, since on each 100volumes of bottoms charged to the bomb, indicating that 84% of the oilwas recovered. This oil had a gravity (A. P. I.) of 17.0 and a viscosityat 210 F., of 263 seconds Saybolt-and is suitable as such forlubrication of heavy machinery or for grease manufacture or the like; ifdesired the oil may be redistilled for production of heavy cylinder oil.The extract from the soap bottoms was acidified with sulfuric acid, andthe organic acids so liberated were washed with water at 200 F. Onvacuum distillation of these acids, 60% of them distilled over atbottoms temperatures ranging from 400 F. to 600 F., under 5 mm. Hgpressure. The distillate teristic odor of crude naphthenic acids.Inspection of this distillate was as follows:

Color 8R Neut. No 123.5 Sap. No 123.5

.These acids may be further purified in various ways, but substantiallyoilfree acids may be ob.- tained by the method described above byincreasing the amount of dilute caustic used for the extraction of thesoaps from the pipe still bottoms, since the oil is relatively much lesssoluble in dilute soap solutions than in concentrated ones.

The present invention is not to be limited to any theory of the chemicalreactions involved in the treatment nor to any particular alkali.

I claim:

1. An improved method for refining heavy hydrocarbon oils by extractioncomprising treating the oil with dilute aqueous caustic soda of up to 5%concentration under pressure high enough to maintain the hydrocarbon oiland caustic solution liquid at the operating temperature, which is above300 F., and below the decompos ing temperature of the hydrocarbon oil,and removing the dilute caustic soda solution and exhad a color of 8Robinson and had the charac-- tracted material from the oil while hot bydecantation.

2. An improved process according to claim 1 in which the treatingsolution is an aqueous solution containing .25 and 5% of caustic soda.

3. Process according to claim 1 in which the dilute caustic soda isrecovered for reuse by cooling and separating the extracted material.

4. An improved process for refining lubricating oil from naphtheniccrudes which are susceptible to serious loss of color on standing,consisting of the steps of bringing the oil into contact with an aqueouscaustic soda solution of from .25 to about 5% while at a temperaturebetween 350 and 500 F., under pressure sufficient to maintain the oiland caustic solution in liquid phase and separating the treating agentfrom the refined oil While hot by decantation.

5. An improved process according to claim 4 in which the treatment isefiected continuously by treating a flowing stream of the oil withcaustic soda solution.

6. Process according to claim 4 in which the treatment is effected bytreating a flowing stream of oil countercurrently with a stream of thecaustic solution.

HANS G. VESTERDAL.

